Production of branched chain alkenes



Patented Dec. 14, 1943 2.336.600 PRODUCTION OF BRANCHED CHAIN ALKENES Eric William Musther Fawcett, Sunbury-on- Thames, England, assignor to Anglo-Iranian Oil Company Limited, London, England, a British ioint-stock corporation ,No Drawing. Application November 28, 1941, Serial No. 420,815. In Great Britain January 11 Claims. (01. zoo-683.2)

This invention relates to the production of branched chain alkenes such as isobutene from normal alkenes, such as normal butenes, or highly branched alkenes from alk enes having a slightly branched structure, or hydrocarbon mixtures containing normal or slightly branched alkenes.

It is known to produce isobutene from butenes found that a considerable proportion of the alkenes is polymerised to yield polymeric products of higher molecular weight.

It is one of the objects of this invention to inhibit polymerisation and to do this it is necessary that there is present in the alkene feedstock a sufiicient proportion of a diluent subin an isomerisation reaction carried out at a temperature between about 250 C. and about 550 C., and at a Pressure not exceeding atmospheres, in which a contact catalyst is used consisting of a phosphoric acid or a phosphoric acid supported upon a carrier such as kieselguhr, and/or compounds of a phosphoric acid with other acidic.

oxides, in the use of which catalyst substantially stantially to inhibit the polymolecular polymerisation reaction without unduly retarding the monomolecular isomerisation reaction. Suitable diluents for this purpose are one or more of the following, namely, nitrogen, hydrogen, water vapour, methane, butane or other saturated hyno polymerisation is stated to take place. The

reaction referred to is carried out in the presence of water vapour for the purpose of maintaining the activity of the catalyst.

The present invention has among its objects to avoid or very substantially to minimise the simultaneous production of polymeric substances, to improve the conditions of the conversion, and to secure high yields of the conversion product.

According to the invention the catalyst employed is an acid phosphate of a-metal of group I, 11, 111, IV, VI, VII or VIII of the periodic system, wmcn has a. phosphorous-metal ratio greater than that of the normal phosphate of the metal. The catalyst may be prepared for use in a solid dry, hard and porous state.

The catalyst may consist of a single acid Phosphate, a' mixture of acid phosphates of more than one metal, or one acid phosphate or more in admixture with a normalphosphate of the same or other metal or metals. The acid phosphate or phosphates may however be supported or incorporated upon carriers advantageously in a porous state for example upon active carbon or ineselguhr. The acid phosphates may be prepared for example by partial neutralisation of phosphoric acid with the metal carbonates or oxides or by addition of phosphoric acid to the normal metallic phosphates.

It is preferred when using asingle' acid catalyst to use an acid phosphate 01 group 1 and advantageously copper, and when using a mixed catalyst to use the acid phosphate of copper together with an acid phosphate of another met- 81 or other metals such as an acid phosphate or phosphates of a metal or metals or group II.

If the normal alkenes are contacted with the catalysts-specified at a temperature within the determined range to enact lsomerlsatlon. I have drocarbon. The precise proportion of diluent to be employed depends on the catalyst used, the nature of the alkene being processed and the reaction conditions, but is generally such that the relative concentrations of alkene and diluent are between 1 part of alkene to 10 parts of diluent and 1 part of alkene to 1 part Of diluent, the parts being measured by volume under the reaction conditions or temperature and pressure. The preferred concentrations of diluent and alkene are generally in the approximate ratio of 1 part of alsene to 2 parts of diluent.

Since the invention is intended for application more particularly to the treatment of alkene fractions obtained in the cracking of mineral oils and. these fractions generally contain a proportion of saturated hydrocarbons lying within the range of diluent concentrations immediately before referred to, the addition of large additional proportions of another diluent is unnecessary in the treatment of such fractions. I have however found that the catalysts hereinbeiore described usually require the presence of a small proportion of water vapour in order thatmaximum activity may be maintained and thus in cases in which the diluent or-main diluent used is not water vapour, I prefer in such cases to add a small proportion of water vapour to the feedstock. By such means high catalyst activity is maintained over an extended period.

The invention comprises the conditions hereinafter described.

The process of conversion or isomerisation according to the invention may be carried out at moderately'elevated temperatures lying within the range C.-600 C., and preferably within the range 250 C.-400 C. and at superatmospheric pressures. Since however increase of pressure in general tends to increase the proportion of polymeric products, it is preferred to operate at pressures below 20 atmospheres.

The invention may be carried out in a batch or continuous process, in liquid or vapour phase, but it is advantageously carried out as a continuous process in the vapour phase, in which a stream of the normal alkene in admixture with a determined proportion of the diluent is passed continuously through a reaction vessel packed with a suitable acid phosphate catalyst prepared as pellets or the equivalents in a solid hard dry and porous state, or in that state supported on a porous carrier. The product stream leaving the reaction vessel, and containing branch chain alkenes may be directly treated by fractionation usually by distillation, to separate partially or wholly the branched chain from the unchanged normal alkenes. The unchanged material may be returned to the reaction system.

In the treatment of normal butene fractions such as are produced in the processing of gases obtained in the cracking of mineral oils, which may contain a considerable proportion of normal butenes and a lower proportion of isobutene, the material may first be submitted to the process of the invention under such conditions as to produce in the treated material an isobutene concentration for example of the order of 10% by volume. The treated material may then be submitted to catalytic polymerisation under known conditions whereby inter-polymerisation of isobutene and normal butenes occurs, with the formation of valuble normally liquid hydrocarbons. The normally gaseous fraction leaving the polymerisation unit rich in normal butenes and practically free from isobutene, may then be recirculated to the isomerisation unit, and so on.

The following are examples of the manner in which the invention may be carried into effect:

Example 1.Normal butene in admixture with an equal volume of water vapour is passed continuously through a reaction vessel containing a copper-cadmium acid phosphate, at a rate equivalent to a contact time of .3 minute.

The catalyst used is prepared as follows:

263 parts of normal cadmium phosphate and 189 parts of copper phosphate are mixed as dry powder, and 218 parts of 90% phosphoric acid worked in, sufiicient water being added to produce a uniform stiff paste. The mixture is then dried at 100 C. for 24 hours and powdered to pass a 10 mesh screen. The powder is then mixed with by weight of graphite, and consolidated into small pellets or small pieces.

The pellets are charged into the reaction vessel, maintained at a'temperature of 300 C., and. atmospheric pressure. The product stream under such conditions was found to contain 12.4% isobutene, while no polymer was produced.

Example 2.Normal butene with an equal volume of water vapour was passed over the catalyst of Example 1 at 294 0., and at atmospheric pressure for a contact time of 1.5 minutes. The product stream contained 31.0% of isobutene, while no determinable proportion of polymer was produced. 1

Example 3.Normal butene in admixtiue with an equal volume of water vapour was contacted with a copper-calcium acid phosphate catalyst at a temperature of 297 C. at atmospheric pressure. The contact time was 1.5 minutes and the product contained 8.5% isobutene, while no polymer was produced. The catalyst employed was prepared according to Example 2 described in the specification of the application Serial No. 357,552.

Example 4.A stream of hydrocarbons containing 54.2% butanes, 39.4% n-butene and 1.9% of isobutene was mixed with water in amount such that the mass ratio of water to hydrocarbon was 0.9. The mixture was passed through a reaction vessel containing the copper-cadmium phosphate catalyst referred to in Example 1 at 350 C. and a pressure of 80 lb./sq. in. at a flow rate equivalent to a contact time of 0.25 minute. Under these conditions 19.0% of the n-butene of the feed stock was converted to isobutene while 2.1% was converted to polymeric hydrocarbons. In this case the main diluent is butane and has for its purpose to suppress polymerisation, while a smaller proportion of Water is used to maintain active isomerisation.

Example 5.Under the same conditions of temperature and pressure and in the use of the same feedstock and catalyst as in Example 4, but using a water-hydrocarbon ratio of 0.1 and a contact time of 0.33 minute, 28.4% of the n-butene of the feedstock was converted to isobutene while 5.4% was polymerised. In this case also the butane serves for the suppression of polymerisation, and the smaller proportion of water serves the purpose of maintaining active polymerisation.

Example 6.Under the same conditions of temperature and pressure and Water concentration and in the use of the same feedstock as in Example 5, but using the copper-calcium phosphate catalyst of Example 3, and a contact time of 0.25 minute, 23.6% of the n-butene of the feedstock was converted to isobutene, and 3.8% to polymers.

The manner of preparation of catalysts employed according to the invention is described in the specifications of the prior Patent No. 2,128,126 and of the application Serial No. 357,552, it being understood that the phosphorous-metal ratio of the catalysts used is greater than that of the normal phosphate.

The catalysts of the Patent No. 2,128,126 are respectively a catalyst advantageously produced from material pelletted from a pulverised cake, being the product of heating and dryin a mixture of cadmium dihydrogen ortho phosphate and ortho phosphoric acid in the molecular proportion or 1:3, or a catalyst in granular form produced by heating a finely divided mixture of cadmium dihydrogen ortho phosphate, a corresponding copper phosphate and ortho phosphoric acid in a molecular ratio of 1:1:4; while the catalysts of the application Serial No. 357,552 are respectively a catalyst produced from material pelletted from a pulverised cake, the product of heating and drying a mixture of calcium phosphate, copper oxide and ortho phosphoric acid in such proportions that no fre acid is present, or a catalyst in pelletted form produced from a finely divided dried cake resulting from the drying of a mixture of bone ash, red copper oxide and ortho phosphoric acid in such proportions that no free acid is present in the catalyst.

I claim:

1. A process for the production of branched chain alkenes from other alkenes including the step of contacting an alkene-containing feedstock at a temperature within the range C.-600 C. with a catalyst comprising an acid phosphate of a metal selected from the group consisting of the metals of the periodic system groups other than the metals of group V, the said metal acid phosphate havingaphosphorousmetal ratio greater than that of the normal phosphate of its metal.

2. The process of claim 1 in which the catalyst is comprised of the said acid phosphate carried upon a porous carrier in a solid, dry, hard and porous state.

3. The process of claim 1 in which the contacting is carried out under a moderate superatmospheric pressure.

4. The process of claim 1 in which the contacting is carried out at a temperature within the range 250 C.-400 C. and at a superatmospheric pressure below 20 atmospheres.

5. The process of claim 1 in which the feedstock contains a gaseous diluent in a proportion by volume of diluent to alkenes within the range 1:1 to 10:1. Y

6. The process of claim 1 in which the feedstock contains a gaseous diluent other than water the reaction mixture of substantially increased iso butene concentration is polymerized catalytically to obtain a, normally liquid hydrocarbon fraction and a normally gaseous fraction rich in normal butenes.

9. A process for the conversion of a, hydrocar-.

bon fraction containing normal alkenes to obtain branched chain alkenes including contacting the fraction at a pressure within the range 1 to 20 atmospheres, a. temperature within the range 250 C.-400 C. and for a time within the range 15 seconds to 90 seconds with a catalyst comprising a mixture of acid phosphates of more than one metal selected from the group consisting of the metals of the periodic system groups other than the metals of group V, each metal acid phosphate having a phosphorous-metal ratio greater than that of the normal phosphate of its metal, said catalyst being prepared b the addition, to a mixture of dry, powdered normal phosphates of the selected metals of phosphoric acid, and consolidating the product in a dry finely divided state together with an inert porous carrier into small pellets.

10. The process of claim 9 in which the catalyst comprises acid phosphates of copper and alcium.

11. The process of claim 9 in which t e catalyst comprises acid phosphates of copper and cadmium.

ERIC WILLIAM MUSTHER FAWCE'I'I'. 

